PNAS: Which sources contribute to differences in air pollution

While air quality has improved significantly over the past 50 years thanks in part to the Clean Air Act, people of color in the United States of all income levels are still exposed to above-average air pollution
.

A team led by researchers at the University of Washington wondered if the Clean Air Act would reduce those discrepancies or if a new approach
was needed.
The team compared two approaches that reflect the main elements of the Clean Air Act and a third, which is less commonly used, to see if it could better address disparities
across the United States.
The researchers modeled each strategy using national emissions data: targeting specific emission sources across the United States; Require regions to comply with specific concentration standards; Or reduce emissions
in specific communities.

While the first two approaches – based on the Clean Air Act – did not eliminate disparities, community-specific approaches eliminated pollution disparities and reduced pollution exposure
overall.

The team published the findings
in the Oct.
24 issue of the Proceedings of the National Academy of Sciences.

"In earlier studies, we wanted to know which pollution sources contributed to these differences, but we found that almost all of them led to unequal exposure
.
So we thought, what is the cost? Here, we tried three approaches to see which best addressed these differences," said
senior author Julian Marshall, a professor of civil and environmental engineering at the University of Washington.
"These two approaches reflect some aspects of the Clean Air Act and are rather weak
in addressing discrepancies.
A third approach is site-specific emissions, which are uncommon but are demanded
by overburdened communities for years.
”

Fine particulate pollution, or PM2.
5, is less than 2.
5 microns in diameter, about 3%
of the diameter of a human hair.
PM2.
5 comes from vehicle exhaust; fertilizers and other agricultural emissions; fossil fuel power generation; forest fires; and the combustion
of fuels such as firewood, oil, diesel, gasoline and coal.
These tiny particles cause heart disease, stroke, lung cancer and other diseases, and are estimated to kill about 90,000 people in the United States each year

The researchers tested these three potential strategies
using the InMAP tool developed by Marshall and other co-authors.
InMAP simulates the chemistry and physics of PM2.
5, including how it forms in the atmosphere, how it dissipates, and how the wind blows it from one place to another
.
The team modeled these methods using national emissions data from 2014 because this is the latest dataset
available at the time of this study.

The researchers looked at how effectively each method was in reducing average pollution exposure for all people, and how disparities
were eliminated for people of color.

While standard methods for emission sources and concentrations have been successful in reducing overall exposure across the country, they have failed to address pollution disparities
.

"Our optimization model is what happens
if we minimize the difference.
If a method cannot solve the difference even if it is optimized, then any real-world application of the method cannot solve the difference," said
Yuzhou Wang, a doctoral student in civil and environmental engineering.
"But we see that even if the emissions reduction for a particular region is less than 1%, the pollution difference that lasts for decades is reduced to zero
.
"

The team said implementing this site-specific approach will require more work to determine which sites are the best targets and to work with local communities to determine how to reduce emissions
.

"Current regulations have improved average air pollution levels, but they do not address structural inequalities and often ignore the voices and experiences of people living in overburdened communities, including their demands
to pay more attention to the sources of pollution affecting their communities," Marshall said.
"These findings reflect historical experience
.
Because of decades of redlines and other racist urban planning, many sources of pollution are more likely to be located in black and brown neighborhoods
.
If we want to address current inequalities, we need a way to
reflect and acknowledge this historical context.
”